1. Field of the Invention
The present invention relates generally to a flush inlet for supersonic aircraft; and, more particularly, to an adjustable two-dimensional, convergent/divergent inlet and inlet passage employing an expansion corner at the upstream leading edge of the inlet entrance so as to permit the inlet to be mounted flush with the external surface of the aircraft; and, wherein the inlet passage is configured in such a way as to cause the generation of a series of weak shock waves as the airstream transits the convergent portion of the inlet passage so as to decelerate the supersonic airflow to transonic or subsonic levels, with the thus decelerated airstream being further decelerated to subsonic levels on the order of Mach 0.4 as it passes through the divergent portion of the inlet passage prior to introduction into the jet propulsion engine. To insure formation of proper shock wave patterns as the supersonic airstream is decelerated, provision is made for removing excess low energy boundary layer air from the inlet passage surfaces, with such extracted low energy boundary layer air that is at pressure levels below freestream static pressure being increased in pressure so as to permit discharge overboard.
In the design of present day supersonic jet aircraft, provision must be made for supplying large quantities of subsonic airflow to supply the requirements of the jet propulsion engine. However, since such aircraft are designed to fly at supersonic speeds, provision must also be made for decelerating the airflow supplied to the engine to the subsonic speeds required by such engines. In general, prior to the advent of the present invention this has been accomplished by employing air inlets which are designed to protrude into the airstream external of the aircraft. Such protruding, and often frontal, air inlets greatly increase the cross-sectional area of the aircraft and deleteriously affect aerodynamic and overall system performance. The present invention is intended to provide a flush inlet for supersonic aircraft which avoids the need to employ either protruding or frontal inlet configurations.
2. Description of the Prior Art
As stated above, most known prior art approaches employed with air inlet designs for supersonic aircraft have employed inlet designs which protrude into the airstream. Typical of such approaches is that disclosed in U.S. Pat. No. 2,971,331-Silverman et al. wherein the patentees disclose an aircraft employing a pair of protruding inlets on opposite sides of the fuselage. Other typical disclosures of protruding inlets are found in U.S. Pat. Nos. 3,104,522-Pennington et al., U.S. Pat. No. 3,417,767-Young, and U.S. Pat. No. 3,643,676-Limage et al. U.S. Pat. No. 2,339,575-Lee, while not relating to supersonic aircraft, is of general interest for its disclosure of a frontal air inlet in combination with diverse complex mechanisms for inducting air from transverse flow streams.
It has further been recognized in the prior art that provision may be made for removing boundary layer air from the inlet air passage. Thus, various systems capable of extracting boundary layer air have been disclosed in the aforesaid Silverman et al. U.S. Pat. No. 2,971,331 and may be found in U.S. Pat. Nos. 2,589,945-Leduc and U.S. Pat. No. 4,000,869-Wong et al.
In general, however, the foregoing typical prior art approaches employ air inlets which protrude into the airstream and which are defined by fixed inlet surfaces. Such prior art approaches do not employ expansion corners at the upstream edge of the inlet and do not provide means for adjusting the inlet cant angle at an expansion corner as a function of the speed of the aircraft. As previously stated, the protruding air inlets of such typical prior art constructions serve to increase the cross-sectional area of the aircraft and, additionally, they seriously degrade the aerodynamic and overall system performance of the aircraft.
It should be noted that flush inlets per se have been recognized in the prior art. See, for example, U.S. Pat. Nos. 2,694,357-Lee and U.S. Pat. No. 2,721,715-Hoadley. The disclosures in the aforesaid Lee and Hoadley patents do not relate to supersonic inlet designs and employ fixed inlet defining surfaces. Such devices simply do not permit of efficient supersonic operation.
One further prior art disclosures of general interest is that found in U.S. Pat. No. 3,624,751-Dettling, a disclosure wherein the patentee contemplates employment of a fluid jet directed into the airstream surrounding the aircraft skin surface for producing a shock wave capable of diverting the airstream into a flush inlet. Again, the inlet is defined by fixed surfaces. No provision is made for optimizing the inlet configuration as a function of the speed of the aircraft, nor are provisions made for decelerating supersonic air inflow prior to introduction into a jet engine.